fo) 
a | 
=~] 
POLYCH-ETA FROM THE N.E. PACIFIC. 
Tasie [I1. 
A. Length of A. B. | C. Total length. 
ieNiosnlacee 12 6 mm. (+) 8 | 26 , 30mm. 
| | 
| { i Peas 
)No. 2...) 0s as | “6 13 6 mm. 
fi ea | veer) oo) pri go thee 
a very small regenerating | 
+ | 5 99, | 9 
| No.3...) stump. | 2 | 12mm. 
if 
= | —— Seen ae 
| | | 
| No. 4...| 12 | 55 mm. (4) | 10 | 10 | 24 mm. 
| } | 
| aca arose oa ee a) ey 
\ | | 22 
INos See 12 | 6mm. (3) a \+15 very small 27 mm. 
segments. 
In this colony (also from Friday Harbour) there are three 
worms complete anteriorly and two fragments, one of which 1s 
commencing regeneration, Of the first-mentioned, however, 
No. 4 has probably lately suffered the loss of posterior segments, 
as shown by the small number of those remaining and the 
moderate total length. No. 5 is interesting from the possession 
of a tail of very small posterior segments following others of 
normal size, and these must represent regeneration after 
autotomy. 
From the comparative rarity of regenerated tails in autotomised 
worms, it is evident that the anterior region is re-formed much 
more quickly than the posterior. With regard to the median 
region, there are two facts which seem to show that regeneration 
of new segments of this type takes place but rarely. These are: 
(1) the great variation in the number of segments (from 
4 to 14), even in individuals with well-developed anterior and 
posterior regions, and 
(2) the absence of segments of two different sizes in the 
region, | have, however, examined one animal alive in its tube 
in which the normal segments of the median region were 
preceded by a single newly formed segment of similar type, but 
only about half the size of the others, I cannot say whether the 
anterior region was fully formed or not, Cases of regeneration 
of median segments then do exist, if but rarely. 
The facts incline me to suggest that asexual generation only 
occurs successfully when fragmentation takes place in the median 
region, that regeneration proceeds both on the anterior and 
posterior surfaces of the plane of rupture, however small a 
number of segments are left on one side, but that these median 
segments usually regenerate anterior or posterior segments, and 
Proc. Zoot. Soc.— 1914, No. LX VI. 66 
